Diagnostics port LMTV

[tennmogger]

I went by the local Allison representative today to make an appointment to bring my LMTV in for diagnostics on the transmission. He showed me the connectors on his test box so I could locate the matching socket on the LMTV. I do not find a port that matches.

What I found is this (photo) and it's about 20 pins larger than his test box.

He mentioned WTEC II and III associated with the test box, but this connector doesn't match either. A search on SS yielded comments about early transmissions with analog test points.

This LMTV may be 'early' version, dated 1994. Did things change any time after that? What diagnostics do I have and how do I use this port?

This transmission works fine but it seems to need the engine to be wound out to max before it shifts. Is that normal? Sure will be hard on fuel this way. I'd like to have it shift at a much lower rpm.

thanks.

 

[Suprman]

The a1 models have advanced diagnostics. The transmissions do wind up and bang into gear most military trans are like that. There may be a fluid pressure adjustment that can soften the shift. Changing to the Allison Dex III may help. There is a connector to the right of the column. I have all of the diag interfaces and some software. But it really dosnt do any good on my trucks. The first lmtv variant has a mechanical engine. The only computer is the trans control behind the keypad. Under the passenger dash there is a vim module for the trans its 2 fuses and 6 bosch relays.

 

[bikeman]

Was just looking at the one I'm holding today and was going to tell you about the additional diagnotstic port just right of the steering column at the bottom of the dash, next to the data panel, but Supr got it.

 

[tennmogger]

Thanks Suprman and Bikeman. The chances that the Allison guys can 'read' my transmission are kinda slim.

As I said before, the trans is working ok, just has a high rpm shift point. I can live with it. The shifts are not bad at all, not tire chirping shifts, just head-bobber shifts.

The more I drive it the better it seems to be shifting (still running the military 15W40 oil).

thanks

Bob

 

[bikeman]

Bob, is your speedometer operating correctly? The only reason I ask, is that Suprman's truck was shifting high, but one of my LMTV mechanics said that a inop or damaged speedo would cause this issue. Just a thought.

 

[Suprman]

No speedo is a bad speed sensor on the trans. Its an over the counter bolt on part. I will look in my diag kit I have a cable that breaks down the big round diag connection into smaller ones. The newer diag setup is usb. The older one is a an rs232 port. It looks kind of like an rgb connection with less pins. Newer laptops dont have it. Maybe one of the mil toughbooks will work. The software runs on win xp.

 

[tennmogger]

My speedo reads about half what it should, say 25 when I'm doing 40, and that is not consistent. Wow, what a great clue Bikeman and Suprman! Makes sense the trans does not shift right if it thinks the speeds are too low. If the speedo is constantly changing then the trans would lose it's shift points.

Any clues where this sender might be located? Of course I'll get into the manual. Better yet, the guys at the Allison shop would know immediately.

thanks,

Bob

 

[Suprman]

Bottom are of trans. It's called engine transmission speed sensor or something transducer depending on which tm you look at. Allison 29543432 is the part.

 

[tennmogger]

Went to Allison shop today and learned a lot.

The rectangular plug to the right of the steering column is the Allison diagnostics connector. It's an old system and 'nothing uses it anymore'. The tech (Ben at Waters Equipment CO) would not give up though.

He knew of a crossover adapter to allow plugging in a NEXIQ Pro-Link IQ reader. That box is not the latest method of diagnostics, and is not what the techs are using now (computer and diagnostics software), but, this box allows plugging into the computer running their latest software! So, by having the right adapter (one intended for off road and construction equipment) plugged into an older but still available diagnostics tool, and then into the newer computer software, THEY COULD READ THIS TRANSMISSON.

It is a WTEC II, as speculated. Ben verified the speed sensor is fine (not bad, and not causing the speedometer inaccuracy) reset the transmission's adaptive learning back to factory spec, and also found that the engine rpm was typically a few hundred rpm below the preferred shift point on some gears. In addition to engine rpm, the preferred shift point varies by gear, and a lot of other inputs like load and road speed. I had no idea these transmissions, even this 1994 version, were as smart as they are.

My transmission was delaying shifting because engine speed was limited by poor linkage adjustment.

By adjusting the throttle linkage to get the engine injection pump to reach it's bump stop (which should be normal operation) the transmission started shifting just fine on test drives.

After we concluded the testing I drove home. The more I drove the better it shifted as it learned how I drive. There were no more reluctant shifts on the way home.

My speedo is still wrong and jumps around a bit, but apparently the transmission speed sensor is not the fault in my case.



Bob

 

[Oxyacetylene]

Went to Allison shop today and learned a lot.

Bob

Can you post more information about the adapter, software, etc? I am also interested in checking the throttle linkage like you describe. On my truck, which is a 93 model, I have noticed that it seems to be finicky about how it shifts. When you first start driving and the engine temp is not all the way up, you either have to wind it out or keep the RPM's in the green range on the tach, then it shifts fine. When the truck is warmed up it shifts much softer and more readily at higher RPM. My truck has a winch, so I can watch the RPM's on the tachometer.

 

[tennmogger]

Sorry but have no more details. Search on NEXIQ and Pro-link and see how many combinations are available. All current software is listed too (and there is a lot). I already searched extensively but did not find the exact model tools the tech had. IMHO it is best to go to Allison and find their best tech and let him figure out how to apply the stuff he has. That cost me $75 plus hours, but well worth it.

I just wanted you guys to know it is possible to diagnose a 3070 at least back to 1994.

 

[tennmogger]

Following up on the speedometer not reading correctly: It is reading correctly now. During a long ride today the speedometer jumped right up to the correct speed and stayed there the remainder of the trip! No idea why it did that.....but I am happy.

This was my first longer ride (about 80 miles) and some harsh roads were encountered. I suspect a bounce may have 'fixed' the speedo.

The engine went into 'over-temp' alarm on a long hard pull. I had been on a steady climb for about 5 miles then a hard climb of 15 to 30 degree incline for a couple of miles. It was near the top of this climb that the temp warning came on.
Temp gauge was reading about 215 degrees (halfway between 210 and 220 marks). It's hot today at 90 plus, there was not a breath of wind, and going was slow (2nd and 3rd gear) so not much air coming into the radiator.

Is it common for an LMTV to overheat?

Lastly, I am hearing a rumble somewhere in the front of the truck (engine or front axle??). The rumble starts as soon as acceleration is topped out and a fixed speed is maintained. The rumble is reduced or stopped if acceleration is increased again. This happens at speeds of maybe 25 mph or higher. Could this be the fan?

Should I be able to turn the fan (with engine stopped) when the engine is cold or hot? I cannot turn the fan at all. I thought I should be able to turn the fan when cold because of the viscous coupling.

Here are some readings with an IR thermometer during this trip, FYI:

Reduction hubs: 120 F
differentials: both were 130 but front pinion was 140.
transmission: 180 F

thanks for any comments,

Bob

 

[Suprman]

Which tires do you have? The Michelin paddle style are agressive and make more road noise than the Goodyears. It could also be a balance issue. Especially if it comes and goes at different speeds. I ran mine fully floored for 20 min or so on the highway it was only around 78 out but the temp never went over around 205 on the gage. Around 200 the fan comes on. There is a dash switch that disables the fan. The truck should not overhead you should be able to run full out with a full load without issue. Did you check your coolant? Do you have heat in the cab if so you know coolant is circulating. There is a thread someone elses fan was stuck on they whacked the clutch a few times and it freed up and worked fine. You will hear the fan coming on its loud. There is a fan disable switch top left on the dash panel. If thats off the fan wont come on.

 

[tennmogger]

Hi Suprman,

Goodyear tires, and they are surprisingly quiet. The noise I am hearing begins abruptly the instant I back off on the pedal after accelerating, and hold a speed. It's a subtle noise, not much above engine and wind noise, but it's there, and it's not tires.

Coolant is fine, thanks. It was so darned hot in the cab the heat could be on but can't say for sure LOL.

The fan has me puzzled. The fan clutch seems to work because I think I have heard it turn on, twice, when hot and crawling around on the farm. At one of those times I did confirm I could turn off the fan, and the roar did stop with the switch off, then roar again with switch back on.

The fan never turned on today because it never got noisy, even when the engine showed overheat. Of course the fan was turning, just not with locked clutch, probably. Seems like the clutch should have locked if the engine was overheating. Maybe a hot engine warning does not specifically trigger the fan clutch to turn on, do you know?

thanks!

Bob

 

[Suprman]

I just dont have enough experience with the trucks to remote diagnose for the overheat. Your best bet would be to follow the tm troubleshooting steps in the manual. Its at the top of the forum under current trucks. Could be something simple
like a bad temp sender or loose wire. You can check actual engine temp with an ir thermometer. It will show a few degrees difference than the flowing coolant temp but should be close. 215 is hot I dont like to see anything over 210 tops.

 

[tennmogger]

I think you are right about loose wire, wonky sensor, or something. The 215 degrees was what I saw on that little temp gauge on the dash. Heck, the needle is 10 deg wide.

I grabbed the IR thermometer and looked around the engine and 180F was the highest I saw on outer surfaces. I forgot to walk around and shoot the radiator but the top of the radiator is hard to get to.

An IR thermometer is a necessity on a newly acquired vehicle! It sure does take a while to get all the bugs worked out. Many of the LMTV's with problems are because no one in the military took the time to work out all the little glitches.

thanks,

Bob

 

[Suprman]

The temp sender is above the alternator if the wire is flopping around zip tie it and make sure it's pushed in all the way. Zip tie up the harness it goes to that runs across the front of the engine.

 

[wyocommo]

I have the exact same overheating issue on my unit. My overtemp light comes on at 230 on the gauge. I do not hear the fan come on when the heat rises, however.

Fan clutch engages when the air is removed as it should. The solenoid that controls the air is working as it should. However, there is a quick exhaust valve between the solenoid and the fan clutch that does not appear to exhausting the air circuit to the clutch as designed. I have not tested the sensor that drives the solenoid.

I have not located the quick exhaust valve yet. Got distracted today replacing the waterpump due to a leak thru the weep hole. I am picking up the new pump tomorrow morning and should get back to troubleshooting the overheat issue tomorrow afternoon.

It might also be a thermostat issue so I am replacing the thermostat while doing the pump.

I have a fairly nice FLIR IR unit to use once I start troubleshooting. I have found lots of electrical problems with it in the past.

Mine must be similar to Suprman's because it gives me the same type of color readouts.

 

[Oxyacetylene]

Mine has started doing this same thing. The temp rises but I never hear the air release to engage the fan clutch. Flipping the fan disengage switch off and on does nothing. I drove it a few weeks ago and after stopping for a while with the engine shut down, it started working again. Drove it a couple nights ago and it wasn't working again.

 

[tennmogger]

Ha ha I am having trouble keeping track or what "it" is